Multip-stage piston type compressor

ABSTRACT

The aim of the invention is to guarantee a high level of impermeability with a low closing force for the sealing elements. To achieve this, the overflow channel ( 19 ) in the valve piston ( 9 ) opens into at least two passages ( 26, 27 ) and the sealing plate of the overflow check valve ( 20 ) that is located in the valve piston ( 9 ) is configured as a freely guided closing membrane ( 28 ) with a limited stroke. The passages ( 26, 27 ) of the overflow channel ( 19 ) have different diameters, are arranged on a graduated circle at a radial distance from the axis of the closing membrane ( 28 ) and are completely covered by said closing membrane ( 28 ).

The Invention relates to a piston compressor according to the preambleof the claim 1.

Such piston compressors are employed in all technical fields, wherethere exists a need for compressed air. Primarily such pistoncompressors are applied in the vehicle industry for pneumatic suspensionand/or air damping.

Such a piston compressor in a two-stage construction is for exampledescribed in the German printed Patent document DE 197 15 291 A1. Thispiston compressor comprises a compressor casing, where a cylindricallow-pressure chamber with a larger low-pressure piston and a cylindricalhigh-pressure chamber with the smaller high-pressure piston are formedin the compressor casing. Here the low-pressure chamber and thehigh-pressure chamber are disposed on a common axis and the low-pressurepiston and the high-pressure piston are formed to a single piecepressure piston with a common piston rod. The low-pressure chamber isfurnished with an intake with an intake check valve, the high-pressurechamber is furnished with an outlet with a discharge check valve and thetwo pressure chambers are connected by an overflow channel, wherein anoverflow check valve is disposed in the overflow channel. A crank pin ofa crankshaft engages with the common piston rod of the low-pressurepiston and of the high-pressure piston at a right angle alignment,wherein the crankshaft is driven for example by an electric motor andwherein the crankshaft transforms the rotary motion of the crankshaftinto a linear motion at the single piece pressure piston. An oscillatingmotion results at the pressure piston from this linear motion.

The intake check valve, the discharge check valve, and the overflowcheck valve have sealing disks made of spring steel, wherein the sealingdisks of the spring steel are attached by a middle screw as is the casewith the intake check valve and with the overflow check valve andwherein the sealing disks of spring steel cover in a sealing way severalflow channels disposed on a partial circle, or which sealing disks areheld by a sideways staggered screw as is the case with the dischargecheck valve and which sealing disks seal off a next disposed flowchannel.

These check valves perform their object only in an insufficient way. Itis to be noted that the metallic sealing disks do not seal sufficiently.This can be traced to the fact that the closure and sealing force of thesealing disks is furnished exclusively by the proper tension of thespring steel. Frequently, a tensioning force acts opposite to theclosure and sealing force, wherein the tensioning force starts from theattachment screw and prevents a smooth resting of the sealing disk in apressure balanced state. Leaks occur also by the fact that fatiguesituations occur at the sealing disk in the course of time and that thesealing disks to not rest perfectly at the sealing surface for thisreason. The sealing disks are usually furnished stronger for balancingthese disadvantageous effects. This in turn increases again theincorporation space of such a sealing disk and decreases the volume ofthe corresponding pressure chamber. Such piston compressor's are thennot very powerful. The higher closure force obtained by reinforcing thesealing disk simultaneously increases however the required opening forcefor the free flow through, which opening force has to be furnished bythe system pressure. This also decreases substantially the degree ofeffectiveness of the piston compressor. It has also become apparent thatthe material of the sealing disks fairly quickly fatigues because of thehigh frequencies of the piston compressor and therefore only a smalllifetime of the sealing disks can be recorded.

Finally, the production of the sealing disks out of spring steel is veryinvolved, since on the one hand the material is hard to work with and onthe other hand high requirements are placed on the quality of thesealing face at the sealing disk.

Therefore it is an object of the present Invention to develop a pistoncompressor of the recited kind, wherein the check valves exhibit a lowclosure force and at the same time assure a high sealing effectiveness.

The object is obtained by the characterizing features of claim 1.

Further embodiments result from the subclaims 2 through 7.

The new piston compressor eliminates the recited disadvantages of thestate-of-the-art.

The Invention is to be explained in more detail by way of an embodimentexample. There is shown for this purpose:

FIG. 1: a two-stage piston compressor in the schematic sectionalpresentation,

FIG. 2: a detail of the piston compressor with the presentation of theintake check valve,

FIG. 3: a detail of the piston compressor with the presentation of theoverflow check valve and of the discharge check valve, and

FIG. 4: a top planar view of the valve inserts belonging to the overflowcheck valve.

According to FIG. 1 a two-stage piston compressor comprises in its maincomponents the piston compressor proper 1, a drive motor 2 and anairdrying unit 3.

A valve casing 4 with a cylindrical inner chamber stepped in itsdiameter belongs to the piston compressor 1, wherein the cylindricalinner chamber is subdivided into a low-pressure chamber 5 with a largerdiameter and in a high-pressure chamber 6 with a smaller diameter. Thelow-pressure chamber 5 is sealingly closed to the outside with a valvecasing floor 7 and the high-pressure chamber 6 is sealingly closed tothe outside with a valve casing cover 8. Here the valve casing cover 8is connected to or formed as a single piece with the casing of theairdrying unit 3. A single piece compressor piston 9 is fitted into theinner chamber of the valve casing 4, wherein the compressor piston 9correspondingly comprises a low-pressure piston 10 with a largerdiameter, a high-pressure piston 11 with a smaller diameter, and acommon piston rod 12. A crank case is formed in the outer region of thepiston rod 12, wherein the connecting rod 13 of the crankshaft 14 of thedrive motor 2 engages in right angle alignment in the crank case. Thelow-pressure chamber 5 and the high-pressure chamber 6 have connectionsamong each other and toward the outside.

An intake check valve 15 is thus disposed according to FIG. 2 in thevalve casing floor 7 of the piston compressor 1, wherein the intakecheck valve 15 connects the low-pressure chamber 5 to the atmosphere.Several intake openings 16 disposed on a common circular path and afirst sealing membrane 17 covering all intake openings 16 belong to theintake check valve 15. Here the sealing membrane 17 is fitted into aninternally disposed sunk bore hole, wherein the sunk bore hole exhibitsa ball shaped or an angular bore hole base. A mushroom like attachmentelement 18 placed in the middle fixes the sealing membrane 17 andmaintains the sealing membrane 17 under a light tension on the base ofthe sunk bore hole. Here this tension entered through the attachmentelement 18 is selected such that the first sealing membrane 17 iscapable of rotation in its position and does not protrude and lift offfrom the intake openings 16 in a pressure balanced state. In addition,the sealing membrane 17 and the attachment element 18 are inserted flushinto the sunk bore hole in order not to lose any volume of thelow-pressure chamber 5.

Thus, there is furthermore disposed a passing through overflow channelor duct 19, wherein the overflow duct 19 connects the low-pressurechamber 5 and the high-pressure chamber 6 to each other. And overflowcheck valve 20 is disposed in the high-pressure side joining region ofthis overflow duct 19 according to FIG. 3, wherein the overflow checkvalve 20 functionally connects to each other or separates from eachother the low-pressure chamber 5 and the high-pressure chamber 6. Forthis purpose the joining region of the overflow duct 19 is expanded to achamber 21 having a cross-section of kidney shape, wherein the kidneyshape follows a circular path.

The overflow check valve 20 comprises a pot collar 22 made out ofplastic, wherein the pot collar 22 with its floor rests on the frontface of the high-pressure piston 11 and rests sealingly at the innerwall of the high-pressure chamber 6. The pot collar 22 is broken out inthe region of the overflow duct 19.

A particularly formed valve support 23, which is inserted fittingly intothe inner space of the pot collar 22 and which is shown in more detailin FIG. 4, furthermore belongs to the overflow check valve 20. Thisvalve support 23 consequently has an outer shape which is directed tothe inner chamber of the pot collar 22. A cylindrical recess 24 isinserted from the side of the high-pressure chamber 6, wherein the axisof the cylindrical recess 24 is disposed remote from the axis of thehigh-pressure piston 11 by a certain eccentricity amount. Thiseccentricity amount as well as the size and the radial position of thecylindrical recess 24 assure, that the cylindrical recess 24 is disposedoverlapping with the chamber 25 having kidney shape. The valve support23 is equipped outside of the cylindrical recess 24 with thedistributedly disposed attachment element 25 for a position determininganchoring with the high-pressure piston 11.

A first passage bore hole 26 with a smaller diameter and a secondpassage bore hole 27 with a larger diameter are disposed in the outerradial region of the cylindrical recess 24, wherein the first passagebore hole 26 and the second passage bore hole 27 exhibit an equal ordifferent distance to the axis of the cylindrical recess 24 and whereinthe first passage bore hole 26 and the second passage bore hole 27 areformed such in their position and their extension that they are disposedoverlapping with the chamber 21 having kidney shape of the overflow duct19. Further passage bore holes can be employed in the same kind inaddition to the first passage bore hole 26 and the second passage borehole 27. A freely resting second sealing membrane 28 is fitted with suchplay into the cylindrical recess 24 that the second sealing membrane 28is freely movable in the rotary direction and in axial direction andsuch that the annular intermediate space between the second sealingmembrane 28 and the inner wall of the cylindrical recess 24 are suitablefor air passage. The neighboring edges of the cylindrical recess 24 andof the second sealing membrane 28 are rounded off or, respectively,performed along broken lines.

Furthermore, the cylindrical recess 24 is covered with a stop grid 29,wherein the stop grid 29 delimits on the one hand the axial stroke ofthe second sealing membrane 28 and on the other hand furnishes asubstantially free passage to the released compressed air stream. Herethe structure of the grid stays is freely selected, wherein thebreakouts in the stop grid 29 are provided of such small size that thesecond sealing membrane 28 cannot become clamped. The breakouts can alsobe of different size.

The high-pressure chamber 6 furthermore exhibits a discharge check valve30 for connecting the high-pressure chamber 6 to a user line. Thisdischarge check valve 13 according to FIG. 3 is disposed between thevalve casing 4 and the valve casing cover 8 and comprises a valve plate31 clamped at the circumference and a third sealing membrane 32. Thevalve plate 31 is sealed relative to the valve casing 4 and relative tothe valve casing cover 8 and is furnished with several outlet openings33 disposed on a common part circle. The third sealing membrane 32 isformed as a ring and correspondingly exhibits a middle flow-through borehole 34. The third sealing membrane 32 is held fixedly between the valveplate 31 and the valve casing cover 8, while the flow-through bore hole34 is formed with its diameter sufficiently smaller as the partialcircle diameter of the diameter of the outlet openings such that theoutlet openings 33 are fully covered by the third sealing membrane 32.

The third sealing membrane 32 is built in without constructivepretension such that a sealing force results only from the materialspecific own proper tension. The first sealing membrane 17 of the intakecheck valve 15, the second sealing membrane 28 of the overflow checkvalve 28 and the third sealing membrane 32 of the discharge check valve30 are made out of plastic and in particular out of an elastic polymer,which elastic polymer is furnished mainly with a high rupturingstrength, which is elastic polymer is highly stable relative totemperature and which elastic polymer exhibits elastic properties withmemory effect.

The rotary motion of the crankshaft 14 driven by the drive motor 2 istransformed through the connecting rod 13 into an oscillating linearmotion during the operation and the oscillating linear motion istransferred to the valve piston 9. Therewith the low-pressure piston 10and the high-pressure piston 11 move in the same way between twooppositely disposed return points and this way form two low-pressurechamber 5 and high-pressure chamber 6 alternatingly changing in volume.

Such an underpressure is generated here while the low-pressure chamberexpands, where the underpressure lifts the first sealing membrane 17 atits outer circumference and allows outer air to flow in through theintake openings 16. This opening pressure results from the sum of thematerial tension of the sealing membrane 17 and the incorporation causedpretension at the sealing membrane 17. At the same time the underpressure closes the second sealing membrane 28 of the overflow checkvalve 20.

A balanced pressure between the low-pressure chamber 5 and theatmosphere occurs at the first sealing membrane 17 at the upper turningpoint of the motion of the valve piston 9, whereby the sealing membrane17 is pressed by the recited forces of the pretensioning onto the intakeopenings 16 and closes the intake openings 16. Lowest passageresistances occur based on the optimum selection of the materialtensions and the incorporation tensions on the one hand duringsuctioning in and on the other hand the first sealing membrane 17 closesin a shortest time after the reaching of the upper turning point. Thisimproves substantially the degree of effectiveness of the pistoncompressor.

The low-pressure chamber 5 is decreased in size with the reverse motionof the valve piston 9 such that the tensioned air in the low-pressurechamber 5 is transported under pressure through the overflow channel 19to the high-pressure chamber 6. Here the air flows initially into thekidney shaped chamber 21 of the overflow duct 19 and charges from therethe second sealing membrane 28 in the region, in the periphery and inthe circumference of the first passage bore hole 26 and of the secondpassage bore hole 27. A first opening force therewith operates throughthe first passage bore hole 26 and a second opening force operatesthrough the second passage bore hole 27 onto the second sealing membrane28, wherein the first opening force and the second opening force bothoperate parallel to each other. These two forces are so different, asare the cross sections of the two passage bore holes 26 and 27. Thefreely disposed second sealing membrane 28 is thereby brought into aninclined position and into a radial rotary motion based on the radialforce components, wherein the radial rotary motion is directed from thesmaller passage bore hole 26 to the larger passage bore hole 27 andwherein the radial rotary motion continuously changes the position ofthe second sealing membrane 28 relative to the two passage bore holes26, 27. This increases decisively the lifetime of the second sealingmembrane 28, since the load of the material of the sealing membrane 28is distributed continuously and therewith a premature overloading ofonly a certain position of the sealing membrane 28 is avoided. Such anoverloading leads quickly to rupturing and to a failure of the overflowcheck valve 20. The freely disposed second sealing membrane 28 presentsonly a lowest resistance to the compressed air stream flowing through.

A balanced pressure between the low-pressure chamber 5 and thehigh-pressure chamber 6 prevails again at the lower return point of themotion of the valve piston 9, wherein the balanced pressure allows theoverflow check valve 20 to close. The closing occurs extremely quick asa reaction based on the free and low friction guiding of the secondsealing membrane 28.

The compressed air enclosed in the high-pressure chamber 6 is displacedthrough the discharge check valve 30 with the motion of the valve piston9 reducing the high-pressure chamber 6. Here the compressed air passesthe discharge openings 33 released by the third sealing membrane 32. Thedischarge check valve 30 again closes in an extremely quick reaction atthe upper return point of the motion of the valve piston 9.

List of Reference Characters

-   1 piston compressor-   2 drive motor-   3 airdrying unit-   4 valve casing-   5 low-pressure chamber-   6 high-pressure chamber-   7 valve casing floor-   8 valve casing cover-   9 compressor piston-   10 low-pressure piston-   11 high-pressure piston-   12 piston rod-   13 connecting rod-   14 crankshaft-   15 intake check valve-   16 intake openings-   17 first sealing membrane-   18 attachment element-   19 overflow duct-   20 overflow check valve-   21 kidney shaped chamber-   22 pot collar-   23 valve support-   24 cylindrical recess-   25 attachment element-   26 first passage bore hole-   27 second passage bore hole-   28 second sealing membrane-   29 stop grid-   30 discharge check valve-   31 valve plate-   32 third sealing membrane-   33 outlet opening-   34 flow-through bore hole

1. Multistage piston compressor comprising a valve casing (4) and ashiftable valve piston (9) formed as a single piece and driven linearlyoscillating by a drive motor (2), wherein the valve piston (9) isfurnished with a low pressure piston (10) and with a high pressurepiston (12), wherein the low pressure piston (10) and the high pressurepiston (11) form at least one volume changeable low-pressure chamber (5)with the intake check valve (15) and with at least one volume changeablehigh-pressure chamber (6) with the discharge check valve (30), andwherein the low-pressure chamber (5) and the high-pressure chamber (6)are connected to each other through an overflow duct (19), wherein anoverflow check valve (20) opening in the direction toward thehigh-pressure chamber (6) is inserted in the overflow duct (19), whereinthe overflow check valve (20) is equipped with a sealing disk,characterized in that the overflow duct (19) joins at least two passagebore holes (26, 27) and wherein the sealing disk of the overflow checkvalve (20) is formed as a loosely guided and stroke limited sealingmembrane (28), wherein the passage bore holes (26, 27) of the overflowduct (19) exhibit different diameters and wherein the passage bore holes(26, 27) are disposed on a common part circle with a radial distance tothe axis of the sealing membrane (28) and wherein the passage bore holes(26, 27) are completely covered by the sealing membrane (28). 2.Multi-stage piston compressor according to claim 1, characterized inthat the sealing membrane (28) is fitted into a recess (24) of a valvesupport (23) and wherein the sealing membrane (28) is covered by a stopgrid (29).
 3. Multistage piston compressor according to claim 2,characterized in that the two passage bore holes (26, 27) are enteredwith the different diameters into the cylindrical recess (24) of thevalve support (23) and have connection to the overflow duct (19),wherein the overflow duct (19) is formed as a kidney shaped chamber (21)in the joining region.
 4. Multistage piston compressor according toclaim 1, characterized in that the sealing membrane (28) comprises anelastic polymer with a high rupture strength, with a high compatibilityto temperature and with memory properties.
 5. Multistage pistoncompressor according to claim 4, characterized in that the intake checkvalve (15) is equipped with a first sealing membrane (17) and whereinthe discharge check valve (30) is equipped with a third sealing membrane(32) and wherein the two sealing membranes (17,32) comprise an elasticpolymer with equal properties.
 6. Multistage piston compressor accordingto claim 5, wherein the intake check valve (15) is equipped with severalintake openings (16) disposed on a partial circle, characterized in thatthe first sealing membrane (17) of the intake check valve (15) is fittedinto a sunk bore hole of the valve case floor (7) with a ball shaped orangular bore hole base and wherein the first sealing membrane (17) isfixed under tension by a centrally placed and mushroom shaped attachmentelement (18), wherein the attachment element (18) immerses only to suchan extent into the sunk bore hole that the attachment element (18)closes flush with the inner face of the valve case floor (7) and whereinthe first sealing membrane (17) is only pretensioned by the attachmentelement (18) to such an extent that the sealing membrane (17) stillremains rotatable.
 7. Multistage piston compressor according to claim 5wherein the discharge check valve (30) is furnished with several outletopenings (33) disposed on a common part circle, characterized in thatthe discharge openings (33) are entered into a valve plate (31), whereinthe valve plate (31) is tensioned between the valve casing (4) and avalve casing cover (8) and wherein the third sealing membrane (32) isformed as a ring and is held with the outer circumference of the thirdsealing membrane (32) without tension between the valve plate (31) andthe valve casing cover (8), wherein the third sealing membrane (32) withits inner circumference covers over the outlet openings (33).